Electrically Conductive Nanocomposite Material and Thermoelectric Device Comprising the Material

ABSTRACT

An electrically conductive composite material that includes an electrically conductive polymer, and at least one metal nanoparticle coated with a protective agent, wherein said protective agent includes a compound having a first part that has at least part of the molecular backbone of said electrically conductive polymer and a second part that interacts with said at least one metal nanoparticle.

FIELD

The present disclosure relates to a composite material that includes anelectrically conductive polymer and a metal nanoparticle; athermoelectric device including the composite material; and athermoelectric device including an electrically conductive polymermaterial.

BACKGROUND

Conventional thermoelectric devices such as thermoelectric generatingdevices or Peltier cooling devices can be fabricated by formingthermocouples from rigid thermoelectric materials such asbismuth-tellurium and disposing a large number of such thermocouples inparallel in the direction of the heat flow. Usually, the thermoelectricmaterial is a bulk material having a columnar shape with a diameter ofseveral millimeters (mm) or a rectangular shape having one side with alength of several mm. In such devices, the cross-section (which iscircular, square, or low oblateness rectangular) is directedperpendicular to the heat flow direction. Recently, attempts have beenmade to produce such thermoelectric devices using thin filmthermoelectric materials.

Thermoelectric devices generate power by having a temperature differencebetween a hot junction and a cold junction. One method of improving theefficiency therefore is to reduce the heat conducted from the hotjunction to the cold junction as much as possible and to create a largertemperature difference between the two junctions. However, inconventional thermoelectric devices, the amount of heat released fromthe thermoelectric material surface is not sufficiently affected.Furthermore, it is sometimes difficult to maintain a large enoughtemperature difference between the two junctions.

Japanese Unexamined Patent Publication No. 2003-133600 describes athermoelectric conversion member that converts heat into electricity byutilizing a temperature difference. The device includes two thin-filmthermoelectric device layers, one having a p-type semiconductor and onehaving an n-type semiconductor. The layers are formed by vapordeposition on a flexible substrate.

Thin film thermoelectric materials can have increased heat release fromthe surface because of the relative increase in the surface area exposedto the outside. However, since the thermal conductivity of generallyused inorganic thermoelectric materials are high (for example, from 1.5to 2.0 W/(m·K) for a Bi—Te alloy (see, J. P. Fleurial et al., J. Phys.Chem. Solids, 49, 1237 (1988)) and 4 W/(m·K) for an Si—Ge alloy (see,Netsuden Henkan Zairyo (Thermoelectric Conversion Material), NikkanKogyo Sha (2005)), a sufficiently large temperature difference betweenthe two junctions often cannot be maintained due to heat transfer fromthe hot junction to the cold junction.

Even though it has low electrical conductivity (about 200 S/cm),polyaniline is widely used in anti-electrostatic applications because ofthe ease in handling and processing the polymer. Increasing itselectrical conductivity could enhance its usage, for example inthermoelectric devices. One method of increasing its electricalconductivity is by combining it with metal nanoparticles.

Japanese Unexamined Patent Publication No. 2004-359742 describes a noblemetal-based catalyst-supported electrically conductive compositematerial produced by performing a polymerization reaction of anelectrically conductive polymer using a noble metal complex as anoxidizing agent. The polymerization simultaneously loads the noblemetal-based complex into the polymer while reducing the noblemetal-based catalyst.

Japanese Unexamined Patent Publication No. 2006-248959 discloses aπ-conjugated molecular compound-metal nanocluster that includes aπ-conjugated molecular compound with metal or metal oxide fine particlesdispersed therein. The nanoclusters are produced by mixing a metal saltand a π-conjugated molecular compound in a solvent and adding sodiumborohydride as a reducing agent.

There still remains a need for electrically conductive polymers thatinclude metal nanoparticles having higher electrical conductivities andincreased compatibility and/or ease of dispersion of the metalnanoparticle.

SUMMARY

Disclosed is an electrically conductive composite material that includesan electrically conductive polymer and at least one metal nanoparticlecoated with a protective agent. The protective agent includes a compoundhaving a first part that has at least part of a molecular backbone ofsaid electrically conductive polymer and a second part that interactswith said at least one metal nanoparticle.

Also disclosed is a thermoelectric device that include a heat resistancesubstrate; a first thermoelectric material including an electricallyconductive composite material, wherein the first thermoelectric materialis disposed in a thin film on said substrate; a second thermoelectricmaterial including an n-type semiconductor or a metal, wherein thesecond thermoelectric material is disposed in a thin film or wire shapeon said substrate, wherein the second thermoelectric material isadjacent to and spaced apart from said first thermoelectric material andwherein said first and second thermoelectric materials togetherconstitute a unit thermocouple; and an electrically conductive materialthat electrically connects an end part of said first thermoelectricmaterial and an end part of said second thermoelectric material, therebyforming a circuit wherein said first thermoelectric material and saidsecond thermoelectric material are alternately electrically connected inseries and both ends of the circuit are opened. The electricallyconductive composite material in the first thermoelectric materialincludes an electrically conductive polymer and at least one metalnanoparticle coated with a protective agent. The protective agentincludes a compound having a first part that has at least part of amolecular backbone of said electrically conductive polymer and a secondpart that interacts with said at least one metal nanoparticle.

Also disclosed is a thermoelectric device that includes a heat resistantsubstrate; a first thermoelectric material including an electricallyconductive polymer, wherein the first thermoelectric material isdisposed in a thin film on said substrate; a second thermoelectricmaterial including an n-type semiconductor or a metal, wherein thesecond thermoelectric material is disposed in a thin film or wire shapeon said substrate, wherein the second thermoelectric material isadjacent to and spaced apart from said first thermoelectric material andwherein said first and second thermoelectric materials togetherconstitute a unit thermocouple; and an electrically conductive materialthat electrically connects an end part of said first thermoelectricmaterial and an end part of said second thermoelectric material, therebyforming a circuit wherein said first thermoelectric material and saidsecond thermoelectric material are alternately electrically connected inseries and both ends of the circuit are opened.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depiction of an exemplary mechanism that couldaccount for the carrier transfer in disclosed composite material.

FIG. 2 is a schematic depiction of an exemplary mechanism that couldaccount for the carrier transfer in a composite material with aconventional protective agent.

FIG. 3 is a schematic depiction of an exemplary thermoelectric device.

FIG. 4 is a schematic exploded depiction of a disclosed stackedthermoelectric device.

DETAILED DESCRIPTION

Disclosed herein is an electrically conductive composite material thatincludes an electrically conductive polymer and metal nanoparticles. Themetal nanoparticles are coated with a protective agent. The protectiveagent is a compound having a first part that has at least part of amolecular backbone of the electrically conductive polymer and a secondpart that interacts with the metal nanoparticle.

Disclosed electrically conductive composite materials can have greatlyincreased electrical conductivity as compared with an electricallyconductive polymer alone, compared with a mixture of an electricallyconductive polymer and a metal nanoparticle without a protective agent,or compared with a mixture of an electrically conductive polymer and ametal nanoparticle with a conventional protective agent that does notinclude both a first part that has at least part of a molecular backboneof the electrically conductive polymer and a second part that interactswith the metal nanoparticle. Thermoelectric devices can have increasedthermoelectric conversion efficiency by creating a larger temperaturedifference between two junctions.

Various polymers can be used as the electrically conductive polymer,including for example, polyacetylene, polyaniline, polythiophene,polypyrrole, polyphenylenevinylene, polythienylenevinylene, derivativesthereof, or the like. Electrically conductive polymers may includesubstituents introduced into the molecular backbone of such anelectrically conductive polymer. The particular polymer can be chosenbased on practical considerations such as, for example, ease of filmformation and stability in the air. In some embodiments, theelectrically conductive polymer can include polyaniline, or derivativesthereof.

Electrically conductive polymers that can be utilized herein can exhibitelectrical conductivity by insulator-metal transition through doping.The electrically conductive polymers can be doped with n-typesemiconductors or n-type semiconductors.

When doping with a p-type semiconductor, a π-electron is removed fromthe conjugated system of the electrically conductive polymer by using adopant called an acceptor. By doing so, a hole is created that can allowmovement along the main chain. Examples of acceptor dopants can includehalogens, Lewis acids, protonic acids, and transition metal halides.Protonic acids are often used as the acceptor dopant. Examples of suchprotonic acids include organic acids such as p-toluenesulfonic acid,camphorsulfonic acid and formic acid; and inorganic protonic acids suchas hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid. Inthe case of polyaniline, a semiquinone radical can be produced by dopingwith protonic acids lacking oxidative ability (such as hydrochloricacid). The polyaniline will therefore exhibit electrical conductivity.

When doping with an n-type semiconductor, an electron is donated to theconjugated system of the electrically conductive polymer by using adopant called a donor. When doing so, an electron can move along themain chain. Examples of donor dopants can include alkali metals andalkylammonium ions.

The protective agent (which can also be referred to as a modifier or acapping agent) is a compound having a first part that has at least apart of the molecular backbone of the electrically conductive polymerand a second part that interacts with the metal nanoparticle. When theprotective agent is coated on the metal nanoparticle surface, the firstpart can contribute to an increase in the compatibility ordispersability of the metal nanoparticle in the electrically conductivepolymer. The protective agent can also interact with metal ions (aprecursor of the metal nanoparticle) which can then be reduced to formthe metal nanoparticle. The protective agent can provide a reaction sitefor reduction and may affect the size of a metal particle growing at areduction site.

The expression “at least a part of the molecular backbone of theelectrically conductive polymer” refers to at least a part of thecharacteristic structure indispensable for constituting the polymer. Forexample, in the case where the electrically conductive polymer ispolyaniline, “at least a part of the molecular backbone of theelectrically conductive polymer” refers to at least a part of thepolyaniline chain, for example, an aminophenyl moiety and a plurality ofaminophenyl moieties polymerized together. In the case of polyaniline,the phrase “at least a part of the molecular backbone of theelectrically conductive polymer”, would also include polyaniline withintroduced substituents, chain ending groups, or the like. The sameapplies to electrically conductive polymers other than polyaniline. Forexample, in embodiments where the electrically conductive polymer ispolythiophene, the phrase “at least a part of the molecular backbone ofthe electrically conductive polymer” includes a thiophene moiety and aplurality of thiophene moieties polymerized together. In embodimentswhere the electrically conductive polymer is polyphenylenevinylene thephrase “at least a part of the molecular backbone of the electricallyconductive polymer” includes a phenyl moiety, a vinylbenzene moiety, anda plurality of phenyl and/or vinylbenzene structures polymerizedtogether.

The second part of the protective agent is one that interacts with themetal nanoparticle. This portion can be capable of forming a coordinatebond, an ionic bond, or the like, to a metal of the metal nanoparticle.Examples of such second parts include for example, a functional grouphaving a coordinating property to a metal, such as a hydroxyl group, acarboxyl group, a sulfonic acid group, an acetylacetonate group, ahalogen group, a nitrile group, a pyrrolidone group, an amino group, anamide group or a thiol group.

Exemplary compounds that can be utilized as the protective agent whenthe electrically conductive polymer is polyaniline include, but are notlimited to 4-aminothiophenol, 2-aminothiophenol, 3-aminothiophenol,2-aminobenzenesulfonic acid, 2-aminobenzoic acid, 3-aminobenzoic acid,4-aminobenzoic acid, 2-aminobenzonitrile, 3-aminobenzonitrile,4-aminobenzonitrile, 2-aminobenzyl cyanide, 3-aminobenzyl cyanide,4-aminobenzyl cyanide, N-phenyl-1,2-phenylenediamine, andN-phenyl-1,4-phenylenediamine. Exemplary compounds that can be utilizedas the protective agent when the electrically conductive polymer ispolythiophene or polythienylenevinylene include, but are not limited to,3-(2-thienyl)-DL-alanine, 4-(2-thienyl)butyric acid,2-(2-thienyl)ethanol, 2-(3-thienyl)ethanol, 2-thiopheneacetic acid,3-thiopheneacetic acid, 2-thiopheneacetonitrile,2-thiophenecarbonitrile, 2-thiophenecarboxamide, 2-thiophenecarboxylicacid, 3-thiophenecarboxylic acid, 2-thiophenecarboxylic acid hydrazide,2,5-thiophenedicarboxylic acid, 2-thiopheneethylamine,2-thiopheneglyoxylic acid, 2-thiophenemalonic acid, 2-thiophenemethanolor 3-thiophenemethanol. Exemplary compounds that can be utilized as theprotective agent when the electrically conductive polymer is polypyrroleinclude, but are not limited to, pyrrole-2-carboxylic acid and1-(2-cyanoethyl)pyrrole. Exemplary compounds that can be utilized as theprotective agent when the electrically conductive polymer ispolyphenylenevinylene include, but are not limited to benzoic acid,benzenethiol, benzenesulfonic acid, 3-vinylbenzoic acid and4-vinylbenzoic acid.

The protective agent may contain a copolymer of a monomer having atleast a part of the molecular backbone of the electrically conductivepolymer and a monomer having a portion that interacts with the metalnanoparticle. For example, when polyaniline is the electricallyconductive polymer, the protective agent may be a copolymer ofN-vinylpyrrolidone (having a pyrrolidone capable of interacting with themetal nanoparticle) andN-phenyl-N′-(3-methacryloyloxy-2-hydroxypropyl)-p-phenylenediamine(having the structure of two aniline moieties).

The metal nanoparticle can be obtained by reducing a metal ion in thepresence of the protective agent. The metal ion can be reduced by, forexample, using a reducing agent such as sodium tetrahydroborate orhydrazine, or an alcohol reduction method. In such embodiments, theparticle diameter of the metal nanoparticles can be from about 1 toabout 100 nm.

The ratio of the number of moles of protective agent to the number ofmoles of the metal nanoparticle may be about 0.1 or more. When the moleratio of protective agent to metal nanoparticles is about 0.1 or more,the metal nanoparticles are generally sufficiently stably dispersed inthe medium (either the reaction mixture and/or the obtained electricallyconductive composite material). The mole ratio can be about 0.5 or more,about 1 or more, about 2 or more, or about 5 or more. The ratio of thenumber of moles of protective agent to the number of moles of the metalnanoparticle may be about 50 or less. When the mole ratio of protectiveagent to metal nanoparticles is about 50 or less, the electricalinteraction between the metal nanoparticles and the electricallyconductive polymer is not inhibited and the electrical conductivity ofthe electrically conductive composite material can be enhanced ascompared with the electrically conductive polymer alone. The mole ratiocan be about 40 or less, about 30 or less, about 20 or less, or about 10or less.

The metal nanoparticles can include simple metals such as gold,platinum, palladium, silver, rhodium, nickel, copper and tin, or analloy of two or more such metals. In embodiments, a metal nanoparticleof gold, platinum, palladium or silver can be used. In embodiments,gold, platinum or palladium can be used because of their relatively highoxidation resistance.

The metal nanoparticles coated with protective agent and theelectrically conductive polymer are physically mixed (for example, witha solvent) to form an electrically conductive composite material.Alternatively, the metal nanoparticles coated with the protective agentcan be mixed in a reaction system containing the electrically conductivepolymer during polymerization of the electrically conductive polymer. Insuch an embodiment, polymerization of the electrically conductivepolymer and mixing of the electrically conductive polymer and the metalnanoparticles can be simultaneously accomplished. Doping of theelectrically conductive polymer may be performed before mixing the metalnanoparticle or may be performed simultaneously with the mixing of themetal nanoparticle.

In embodiments, the electrically conductive polymer can include about0.01 wt % or more of metal nanoparticles based on the weight of theelectrically conductive polymer. In embodiments where the metalnanoparticle content is about 0.01 wt % or more (based on the weight ofthe electrically conductive polymer), the electrical conductivity of theelectrically conductive composite material can be enhanced. Theelectrically conductive polymer can include about 0.05 wt % or more,about 0.1 wt % or more, about 0.5 wt % or more, about 1 wt % or more,about 2 wt % or more, or about 5 wt % or more of metal nanoparticlesbased on the weight of the electrically conductive polymer. Theelectrically conductive polymer can include up to about 95 wt %, up toabout 90 wt %, up to about 85 wt %, up to about 80 wt %, or up to about75 wt % of metal nanoparticles based on the weight of electricallyconductive polymer. In embodiments where the electrically conductivecomposite material is to be used as a p-type thermoelectric material,the electrically conductive composite material may be about 30 vol % orless of metal nanoparticles. For example the electrically conductivecomposite material may be about 25 vol % or less, about 20 vol % orless, or about 10 vol % or less of metal nanoparticles. The electricallyconductive composite material typically includes at least about 0.01 vol%, at least about 0.05 vol %, at least about 0.1 vol %, at least about0.3 vol %, at least about 0.5 vol %, at least about 0.8 vol %, or atleast about 1 vol % of metal nanoparticles.

The Seebeck coefficient of a metal is generally low and therefore,addition of the metal nanoparticle in relatively large amounts can leadto a reduction of the Seebeck coefficient of the electrically conductivecomposite material. However, when the metal nanoparticles are utilizedin amounts as described herein, the reduction of the Seebeck coefficientof the electrically conductive polymer can be minimized in order tostill increase the electrical conductivity.

Disclosed electrically conductive composite materials can be utilized invarious shapes. For example, an electrically conductive compositematerial film may be formed by dissolving the electrically conductivecomposite material in m-cresol or the like, applying the solution onto asubstrate such as a glass substrate or polymer film (by methods such asbar coating, screen printing or spin coating) and drying the coating. Aplurality of the films may be stacked. Alternatively, the film may bestretched to align the orientation of the electrically conductivepolymer and thereby further increase the electrical conductivity.

FIG. 1 Shows a mechanistic explanation for electrically conductivepolymers composites with the protective agent that includes both a firstpart that has at least part of the molecular backbone of theelectrically conductive polymer and a second part that interacts withthe at least one metal nanoparticle. Although not wishing to be bound bytheory, a possible mechanistic explanation for the increase in theelectrical conductivity of disclosed electrically conductive compositematerials is depicted in FIG. 1.

Electrical conductivity is typically greatly affected by carriertransfer (carrier hopping) between molecular chains of the electricallyconductive polymer. Conventionally employed protective agents (i.e.,protective agents without a first part that has at least part of themolecular backbone of the electrically conductive polymer but with asecond part that interacts with the at least one metal nanoparticle) aregenerally insulating organic compounds, which in many cases are not verycompatible with electrically conductive polymers. FIG. 2 illustrates themechanism for a conventional protective agent. As shown in FIG. 2, evenwhen a metal nanoparticle 220 coated with a conventional protectiveagent 210 is dispersed in an electrically conductive polymer 230 aninsulating region 240 is formed on the metal nanoparticle 220 surface.This inhibits carrier transfer (carrier hopping) of a positive charge250 flowing in the electrically conductive polymer 230 to anotherelectrically conductive polymer 230 through the surface or bulk of themetal nanoparticle 220.

On the other hand, protective agents as disclosed herein include a firstpart that includes at least a part of the molecular backbone of theelectrically conductive polymer and therefore, are highly compatiblewith the electrically conductive polymer. FIG. 1 shows that by virtue ofthis compatibility, the disclosed protective agent 10 can attractmolecular chains of two or more electrically conductive polymers 30 tothe metal nanoparticle 20 thereby allowing the molecular chains to comeclose together. As shown by the arrow in FIG. 1, a positive charge 50,flowing in the electrically conductive polymer 30, is encouraged toundergo carrier transfer through the surface or bulk of the metalnanoparticle 20 or can undergo direct carrier transfer between twospatially close molecular chains. As a result of such a mechanism, theelectrical conductivity of the electrically conductive compositematerial can be increased.

The disclosed electrically conductive composite materials can beutilized in various electric/electronic applications. Specific examplesof applications include anti-electrostatic technology,anti-electromagnetic wave technology, electrical connection technology,capacitors, secondary batteries and actuators.

Disclosed electrically conductive composite materials that are p-typethermoelectric materials can be used for thermoelectric generationutilizing waste heat of a factory, an incinerator or the like, or wasteheat of electrical equipment. Disclosed p-type electrically conductivecomposite materials can also be used as temperature sensors orthermoelectric cooling devices (Peltier device).

Disclosed herein are thermoelectric devices that include (a) a heatresistant substrate, (b) a first thermoelectric material that includesan electrically conductive polymer, wherein the first thermoelectricmaterial is disposed in a thin film on the substrate, (c) a secondthermoelectric material that includes an n-type semiconductor or ametal, wherein the second thermoelectric material is disposed in a thinfilm or wire shape on the substrate, wherein the thin film or wire shapeis adjacent to and spaced apart from the first thermoelectric material,and wherein the first and second thermoelectric materials togetherconstitute a unit thermocouple together, and (d) an electricallyconductive material that electrically connects an end part of the firstthermoelectric material and an end part of the second thermoelectricmaterial forming a circuit where the first thermoelectric material andthe second thermoelectric material are alternately electricallyconnected in series and both ends of the circuit are opened. In someembodiments, the first thermoelectric material includes a compositematerial that includes both an electrically conductive polymer and atleast one metal nanoparticle coated with a protective agent. Theprotective agent includes a compound having a first part that has atleast part of a molecular backbone of said electrically conductivepolymer and a second part that interacts with said at least one metalnanoparticle.

In embodiments, the first thermoelectric material can be disposed in athin film, so that the surface area exposed to the external environmentof the thermoelectric device can be made relatively large. The thermalconductivity of the electrically conductive polymer in the firstthermoelectric material is lower than that of conventional inorganicthermoelectric materials. Because of this, heat conducted from a hotjunction to a cold junction can be efficiently dissipated to theexternal environment between those junctions and the temperaturedifference between the two junctions can be maintained. This canincrease the thermoelectric conversion efficiency of the thermoelectricdevice.

The heat resistant substrate can be any substrate that does not deformor collapse at the operating temperatures of the thermoelectric device.Generally, the operating temperature of the thermoelectric device is notmore than about 200° C. The substrate can either be an insulatingmaterial or an electroconductive material. In embodiments where anelectroconductive material is used, an insulating film can be providedon the surface to avoid electrical contact between the substrate and thethermoelectric material. The shape, size, and the like of the substrateare not particularly limited. In embodiments, the substrate may berectangular or square so that the devices can be easily arranged. Inembodiments where the substrate is a square or rectangle, the substratemay have a length of about 10 to about 1,000 mm and a width of about 10to about 1,000 mm.

In embodiments where it is desired that the device be flexible, flexiblepolymer films such as polyimide or polyethylene terephthalate can beused as the substrate. In such embodiments, the flexible substrate mayhave a thickness of about 5 μm or more; in embodiments about 10micrometers (μm) or more. Flexible substrates having a thickness ofabout 5 μm or more are generally sufficiently strong. The flexiblesubstrate may have a thickness of about 2 mm or less; or in embodimentsabout 1 mm or less. Flexible substrates having thicknesses of about 2 mmor less provide sufficient flexibility to allow bending or deforming ofthe device. Such flexibility can allow the device to be bent or deformedso as to fit a limited installation space. Such flexibility can furtherenhance the heat release by affording appropriate arrangement of a hotjunction and/or a cold junction. A flexible thermoelectric device canalso be contacted with a heat source having a curved surface by allowingthe device shape to conform to the curved surface, this can minimize theheat transfer loss between the heat source and the thermoelectricdevice.

The first thermoelectric material contains an electrically conductivepolymer and is disposed in a thin film on the substrate. The thin filmenables efficient heat release from the surface of the thermoelectricmaterial. Various polymers can be utilized as the thermoelectricmaterials, including polyacetylene, polyaniline, polythiophene,polypyrrole, polyphenylenevinylene, polythienylenevinylene, derivativesthereof, and the like. In embodiments, polyaniline, polythiophene,polypyrrole, polyphenylenevinylene, polythienylenevinylene, derivativesthereof, and the like can be used due to their ease of film formationand air stability. In embodiments, polyaniline can be used.

Polyaniline generally has a thermal conductivity from 0.02 to 0.24W/(m·K) (27° C.) (see, H. Yan, et al., J. Therm. Anal. Cal., 69, 881(2002)) and polyphenylenevinylene generally has a thermal conductivityfrom 0.05 to 0.16 W/(m·K) (25° C.) (see, Y. Hiroshige, et al., Synth.Met., 157, 467 (2007)). As seen from these values, the thermalconductivity of the electrically conductive polymer is fromapproximately 1/10 to 1/100 of that of conventional thermoelectricmaterials and therefore, the heat conducted from a hot junction to acold junction without dissipating from the surface can be greatlyreduced.

The electrical conductivity of the first thermoelectric material may beenhanced by using an electrically conductive composite material asdisclosed herein as the first thermoelectric material. As disclosedabove, an electrically conductive composite material includes anelectrically conductive polymer in combination with a metalnanoparticle. The metal nanoparticle can be coated with a protectiveagent, which is a compound having a first part that is at least a partof the molecular backbone of the electrically conductive polymer and asecond part that interacts with the metal nanoparticle. Use of even asmall amount of such a protective agent coated nanoparticle can greatlyincrease the electrical conductivity while at the same time minimizingthe reduction in the Seebeck coefficient. This can lead to increasedthermoelectric conversion efficiency for a thermoelectric device asdisclosed.

In embodiments, a first thermoelectric material can have a ratio ofoblateness of the cross section (length of the long side ofcross-section/film thickness) perpendicular to the direction of heatflow (direction running from a hot junction toward a cold junction) ofthe thermoelectric device of about 5 or more; and in embodiments ofabout 10 or more. For example, assuming that the ratio of oblateness is10, the surface area of the thermoelectric material becomes about 4times or more than the surface area of a thermoelectric material havingthe same cross-sectional area with a circular or square cross-section.Therefore, by setting the ratio of oblateness to be about 5 or more, thesurface area exposed to the external environment of the firstthermoelectric material can be made sufficiently large, which canefficiently dissipate heat conducted from a hot junction to a coldjunction from the surface of the first thermoelectric material to theexternal environment.

In embodiments where a flexible substrate is utilized, the thickness ofthe first thermoelectric material may be about 1 μm or more; and inembodiments, about 5 μm or more. When the thickness of the firstthermoelectric material is about 1 μm or more, breaking of thethermoelectric material by bending or deformation of the thermoelectricdevice can be prevented. In embodiments where a flexible substrate isutilized, the thickness of the first thermoelectric material may beabout 10 mm or less; and in embodiments about 5 mm or less. When thethickness of the first thermoelectric material is about 10 mm or less,sufficient flexibility can be imparted to the thermoelectric device.

The first thermoelectric material can have various shapes, including astrip, a rectangle, or a square. The length along the heat flowdirection of the first thermoelectric material may be selected dependingon the dimensions of the substrate, the shape of the substrate, and thelike. In embodiments, the length along the heat flow direction of thefirst thermoelectric material may be from about 10 to about 1,000 mm.

The second thermoelectric material is disposed on the substrate adjacentto and spaced apart from the first thermoelectric material. The firstand second thermoelectric materials together constitute a unitthermocouple. The second thermoelectric material includes an n-typesemiconductor or metal. Generally, n-type semiconductors or metals thatare employed in general thermoelectric devices can be used. Examples ofn-type semiconductors or metals include alloy-based thermoelectricmaterials (such as scutterdite compounds, silicide-based compounds,half-heusler metals and boron compounds), oxide-based thermoelectriccompounds (such as zinc oxide compounds, titanium oxide compounds andnickel oxide compounds), and metals (such as copper, nickel andplatinum).

The second thermoelectric material is disposed in a thin film or wireshape on the substrate. In embodiments where the second thermoelectricmaterial is a thin film, the oblateness, thickness, shape and lengthalong the heat flow direction of the second thermoelectric material maybe the same as those of the first thermoelectric material or may bedifferent. The oblateness, thickness, shape, and length may be chosenbased on the arrangement pattern of unit thermocouples, the electricconductivity, the Seebeck coefficient, the thermal conductivity, and thelike of the second thermoelectric material. A thin film of a secondthermoelectric material may be, for example, formed by vapor deposition,may be a foil, or may be a film formed by dispersing the above-describedn-type semiconductor or metal in a resin. In embodiments where thesecond thermoelectric material is in the shape of a wire, the secondthermoelectric material may be disposed such that the entire wire is incontact with the substrate or the wire contacts the substrate only at aportion that is electrically connected to the first thermoelectricmaterial. The length and diameter (or cross-sectional area) of the wirecan be chosen based on the arrangement pattern of unit thermocouples,and the electric conductivity, Seebeck coefficient, thermal conductivityand the like of the second thermoelectric material.

The thickness of the second thermoelectric material may be chosen sothat it does not impair the flexibility of the thermoelectric device. Inembodiments that utilize an n-type semiconductor in a thin film as thesecond thermoelectric material, the thickness thereof may be about 0.5mm or less. In embodiments that utilize a metal in a thin film as thesecond thermoelectric material, the thickness thereof may be about 1 mmor less. In embodiments where the second thermoelectric materialincludes a metal, and is in the form of a wire, the diameter thereof maybe about 1 mm or less. In embodiments where the second thermoelectricmaterial is a film including a resin having an n-type semiconductor or ametal dispersed therein, the thickness can be increased due to theflexibility of the resin.

An end part of the first thermoelectric material and an end part of thesecond thermoelectric material in proximity thereto are electricallyconnected to form a unit thermocouple with the remaining two end partsbeing unconnected. In embodiments where one unit thermocouple iscontained in a thermoelectric device, the unit thermocouple can beregarded as a simple circuit where the first thermoelectric material andthe second thermoelectric material are electrically connected in seriesand the remaining two end parts are opened as a terminal. The electricalconnection between the end parts of the first and second thermoelectricmaterials may be performed using an electrically conductive materialsuch as solder, electrically conductive paste or anisotropicelectrically conductive film. Before performing the electricalconnection by using such an electrically conductive material, a metalthin-film layer may be provided on the connection portion of the firstthermoelectric material and/or the second thermoelectric material toreduce the electrical contact resistance between the electricallyconductive material and the thermoelectric material. The optional metalthin film layer may be formed by sputtering, vapor deposition, or thelike.

In embodiments where a plurality of unit thermocouples are disposed onthe substrate, a single unit thermocouple has the unconnected end partof a first thermoelectric material electrically connected to theunconnected end part of a second thermoelectric material of an adjacentunit thermocouple; and the unconnected end part of a secondthermoelectric material is electrically connected to the end part of afirst thermoelectric material of a second adjacent unit thermocouple. Inthis way, a circuit is formed on the substrate, where a firstthermoelectric material and a second thermoelectric material arealternately electrically connected in series and both ends of thecircuit are opened. Electrical connection of a plurality of unitthermocouples can be performed using the above-described electricallyconductive material.

A stacked thermoelectric device can also be formed. A stackedthermoelectric device can be formed by stacking a plurality ofsubstrates, each substrate having disposed thereon one unit thermocoupleor a plurality of unit thermocouples. Stacked thermoelectric devices canbe advantageous when a high output voltage is required. Electricalconnection between two unit thermocouples on separate substrates may beperformed using copper wire in combination with the above-describedelectrically conductive material or may be performed through aconnection pattern previously formed on the substrate, such as a circuitpattern formed on a substrate by using a resist and plating.

In embodiments, a material having high thermal conductivity may beprovided on the joint portion of the first and second thermoelectricmaterials to cover the joint portion. This can provide better contactwith the heat source. In embodiments, a protective film may be providedon the surface of the device. This can provide mechanical protection orreinforcement of the thermoelectric material surface, rust prevention,insulation assurance, or the like.

FIG. 3 shows a thermoelectric device 60 that includes a substrate 70.Positioned on the substrate 70, is a first thermoelectric material 80disposed as a strip-like thin film, a second thermoelectric material 90disposed as a strip-like thin film adjacent to and spaced apart from thefirst thermoelectric material 80, an electrically conductive material100 alternately electrically connects the first and secondthermoelectric materials in series, and a lead wire 111 connected toeach of two terminals 110 of the formed circuit.

To fabricate such a device, the first thermoelectric material 80 can bedispersed or dissolved in a solvent, and the liquid dispersion orsolution can be applied to the substrate 70 (by for example bar coating,screen printing, spin coating or ink jetting), and then dried to form athin film. During the coating, a masking tape or the like may be used toprevent the first thermoelectric material 80 from being applied to anunnecessary portion of the substrate. In the case of using screenprinting, inkjet printing or the like, the first thermoelectric material80 can be applied in the desired shape or pattern (in FIG. 3, astrip-like shape) directly on the substrate 70. In order to increase theadherence between the first thermoelectric material 80 and the substrate70, the surface of the substrate 70 may be subjected to physical surfacemodification such as plasma treatment, flame treatment, electron beamtreatment and corona treatment, or chemical surface modification using acoupling agent or the like. In other embodiments, a thin film of thefirst thermoelectric material 80 can be separately produced and then cutinto a desired shape (for example a strip-like shape). This thin filmcan then be disposed on the substrate 70 by using an adhesive or thelike. In embodiments where the substrate 70 is an adhesive tape, thethin film may be attached directly to the adhesive surface thereof.

The second thermoelectric material 90 can be disposed as a strip-likethin film directly on the substrate 70 by using a mask with a vaporphase process (such as sputtering or vapor deposition). Similar to thefirst thermoelectric material 80, a strip-like thin film or linear formsuch as wire of the second thermoelectric material 90 may be separatelyproduced and then disposed on the substrate 70 by using an adhesive orthe like.

Electrical connection in a single unit thermocouple or between unitthermocouples may be established using an electrically conductivematerial 100 such as solder, electrically conductive paste oranisotropic electrically conductive film. Soldering using flux, coatingof an electrically conductive paste, or application of an anisotropicelectrically conductive film in an appropriate size on the connectionportion can all accomplish electrical connection. Some of theseelectrical connection portions, a group of junctions 101 (arranged onone side, in FIG. 3, the bottom side of the thermoelectric device 60)can be used as hot junctions and some of the others, a group ofjunctions 102 (arranged on the opposite side, in FIG. 3, the top side ofthe thermoelectric device 60), can be used as cold junctions, or viceversa.

To each of the terminals 110 of the thermoelectric device 60thus-obtained, a lead wire 111 for connection to an external circuit maybe attached using the above-described solder, electrically conductivepaste or the like.

The stacked thermoelectric device 61 schematically shown in an explodedperspective view in FIG. 4 includes, on a substrate 70, a firstthermoelectric material 80 that is provided as a rectangular thin filmand a wire-shaped second thermoelectric material 90 electricallyconnected to the end part of the first thermoelectric material by anelectrically conductive material 100. A lead wire 111 is attached toeach of the terminals 110 present on the outermost and lowermost layersof the stacked thermoelectric device 61. For the sake of simplicity inFIG. 4, all constituent elements are not labeled with a referencenumeral.

The first thermoelectric material 80 can be disposed in the same manneras in the thermoelectric device depicted in FIG. 3. In the embodimentdepicted in FIG. 4, a wire-shaped second thermoelectric material 90 suchas copper wire is bonded to two end parts at diagonal corners of thefirst thermoelectric material 80 by using an electrically conductivematerial 100 such as electrically conductive paste. A plurality of unitthermocouples can be formed with first thermoelectric materials 80 andsecond thermoelectric materials 90 alternately electrically connected inseries. Electrical connection between a certain layer and the underlyinglayer can be performed at the same time as the formation of a unitthermocouple by disposing the second thermoelectric material 90 acrossthose two layers. Similarly to FIG. 3, a group of junctions 101 arrangedon one side (in FIG. 4, the front side) of the stacked thermoelectricdevice 61 can be used as hot junctions, and a group of junctions 102arranged on the opposite side (in FIG. 4, the back side) can be used ascold junctions, or vice versa.

Disclosed thermoelectric devices can be used for power generationutilizing a temperature difference, for example, for thermoelectricgeneration utilizing waste heat of a factory, an incinerator or the likeor waste heat of electrical equipment. In general, disclosedthermoelectric devices generate electricity by contacting the electricalconnection portion(s) (hot junction) on one side with a high-temperatureheat source and contacting the electrical connection portion(s) (coldjunction) on the opposite side with a low-temperature heat source.Disclosed thermoelectric devices can release high levels of heat fromthe surface of the device and only conduct small quantities of heat froma hot junction to a cold junction and therefore can maintain a largetemperature difference between the hot junction and the cold junction.Therefore, depending on the usage, sufficient thermoelectric conversioncan be performed even though the cold junction is not in contact with alow-temperature heat source.

Disclosed thermoelectric devices can also be used as thermoelectriccooling devices (Peltier devices) where the high-temperature portion iscooled by passing electricity to the thermoelectric device while the hotand cold junctions are in contact with a high-temperature portion and alow-temperature portion, respectively.

EXAMPLES

Representative Examples are described in detail below, but it will beapparent to one skilled in the art that changes and modifications can bemade in the following embodiments within the scope of the presentdisclosure.

All chemicals were obtained from Wako Pure Chemical Industries, Ltd.(Osaka, Japan) unless indicated otherwise.

Example 1 (1) Synthesis of Gold Nanoparticle

A gold nanoparticle having p-aminothiophenol (p-ATP) as a protectiveagent was synthesized as follows. A 1.0 mM ethanol/water (volumeratio=1:1) solution of p-ATP was prepared. This solution was placed in anitrogen atmosphere and tetrachloroauric(III) acid tetrahydrate wasadded to the solution to give a tetrachloroauric(III) acid concentrationof 1.0 mM. The solution had a mole ratio of p-ATP to gold ion (Au³⁺) of1:1. The solution was stirred (in the nitrogen atmosphere) whileshielding it from light and was then subjected to reduction of the goldions by drop wise addition of an aqueous solution of sodiumtetrahydroborate as a reducing agent. This caused the solution to turnblack. This solution was dried, washed with water and then dried againto obtain a black powder. X-ray diffraction measurements of the blackpowder showed a peak attributable to crystalline gold. From the shape ofthe peak, the size of the crystal was determined to be 16 nm. ICPanalysis revealed that the content of gold was 75 wt %.

(2) Polymerization of Polyaniline

Polyaniline (PANi) was synthesized using an oxidative polymerizationmethod as follows. 9.38 g (0.10 mol) of aniline (obtained by distillingcommercially available aniline under reduced pressure) was mixed with100 mL of 1 M hydrochloric acid in an ice bath for 3 hours. Thereafter,100 mL of an aqueous solution having 28.53 g (0.125 mol) ammoniumpersulfate dissolved therein was added drop wise to the mixed solutionwhile stirring at −8° C. over 5 hours. Stirring was continued at −8° C.for 15 hours, and the obtained precipitate was recovered. Theprecipitate was washed, rinsed with aqueous ammonia, washed again andthen dried to obtain PANi at a yield of 84.9%. The weight averagemolecular weight of the obtained PANi was 6.7×10⁴ amu, and thepolydispersity was 1.3. UV-Vis spectroscopy confirmed that the PANi hadan emeraldine structure.

(3) Combining p-ATP-Coated Gold Nanoparticles and ElectricallyConductive PANi

248.3 mg of PANi, synthesized as above, and 290 mg of camphorsulfonicacid (CSA) were mixed in an agate mortar. A solution obtained bydispersing 1.7 mg of p-ATP-coated gold nanoparticle in 1.25 g ofm-cresol was added to the mixture and mixed. 23.55 g of m-cresol wasthen added and thoroughly mixed. At this point, the content of goldbased on PANi was 0.5 wt %.

The solution was coated on a glass substrate and dried to obtain a PANifilm. The PANi film was cut into an appropriate size, a platinum wirewith a diameter of 0.1 mm was connected, and the electrical conductivitywas measured using a four-terminal method. An electrically conductivepaste, XC-32 (Fujikura Kasei Co., Ltd., Tokyo, Japan) was used for theelectrical connection. The Seebeck coefficient of the PANi film(separated from the glass substrate) was measured using a Mobile Seebeckdevice (ai-Phase Co., Ltd., Tokyo, Japan). The results are shown inTable 1.

Example 2 and Example 3

A p-ATP-coated gold nanoparticle obtained as detailed in Example 1 wascombined with electrically conductive PANi as detailed in Example 1except that the gold content based on PANi was changed to 1.1 wt %(Example 2) or 2.1 wt % (Example 3). The electric conductivity andSeebeck coefficient were measured as detailed in Example 1, and theresults are shown in Table 1.

Example 4

A p-ATP-coated gold nanoparticle was synthesized as detailed in Example1 except that the mole ratio of p-ATP to gold ion (Au³⁺) in the solutionbefore reduction of the gold ion was 5:1. X-ray diffraction measurementsof the p-ATP-coated gold nanoparticles obtained showed a peakattributable to crystalline gold. From the shape of the peak, it wasdetermined that the size of the crystal was 2.5 nm. ICP analysisrevealed that the content of gold was 69 wt %. This p-ATP-coated goldnanoparticle was combined with electrically conductive PANi as detailedin Example 1. The electric conductivity and Seebeck coefficient weremeasured as detailed in Example 1, and the results are shown in Table 1.

Example 5

A p-ATP-coated gold nanoparticle obtained as detailed in Example 4 wascombined with electrically conductive PANi as detailed in Example 1except that the gold content based on PANi was 1.0 wt %. The electricconductivity and Seebeck coefficient were measured as detailed inExample 1, and the results are shown in Table 1.

Comparative Example 1 Performance Evaluation of Electrically ConductivePolymer PANi Alone

PANi (250 mg) obtained as detailed in Example 1 and 290 mg of CSA weremixed in an agar mortar, and 24.8 g of m-cresol was added thereto andmixed thoroughly. This solution was coated on a glass substrate anddried to obtain a PANi film. The electric conductivity and Seebeckcoefficient were measured as detailed in Example 1, and the results areshown in Tables 1, 2 and 4.

Comparative Example 2 Metal Nanoparticle-PANi Composite Using AnilineMoiety-Free Protective Agent

A gold nanoparticle having polyvinylpyrrolidone (PVP) as a protectiveagent was synthesized as follows. A 1.0 mM ethanol/water (volumeratio=2:8) solution of PVP K30 was prepared. To this solution,tetrachloroauric(III) acid tetrahydrate was added to give atetrachloroauric(III) acid concentration of 1.0 mM. The solution had amole ratio of PVP to gold ion (Au³⁺) of 1:1. The solution was stirred ina nitrogen atmosphere and was shielded from the light. The solution wasthen heated to 80° C. to create a reflux state. A 0.1 M sodium hydroxidesolution was added drop wise so that the sodium hydroxide molar amountwas four (4) times that of the gold ion (Au³⁺). Immediately after thedrop wise addition, the solution turned reddish black. This solution wasdried, washed with water and dried again to obtain a black powder. X-raydiffraction measurements of the black powder showed a peak attributableto crystalline gold. From the shape of the peak, the size of the crystalwas found to be 4.9 nm. ICP analysis revealed that the content of goldwas 77 wt %.

The PVP-coated gold nanoparticle was combined with electricallyconductive PANi as detailed in Example 1 except that the gold contentbased on PANi was 2.0 wt %. The electric conductivity and Seebeckcoefficient were measured as detailed in Example 1, and the results areshown in Tables 1 and 4.

TABLE 1 Comparative Example Example 1 2 3 4 5 1 2 Protective Agent:Gold1:1 1:1 1:1 5:1 5:1 — 1:1 (Mole ratio) Gold content in PANi 0.5 1.1 2.10.5 1.0 0 2.0 (wt %) Electric conductivity 337 338 356 382 369 191 219(S/cm) Seebeck coefficient 13.2 13.6 12.9 13.0 13.4 13.4 11.8 (μV/K)

Example 6

A p-ATP-coated gold nanoparticle was synthesized as detailed in Example1 except that the mole ratio of p-ATP to gold ion (Au³⁺) beforereduction of the gold ion was 20:1. X-ray diffraction measurements ofthe obtained p-ATP-coated gold nanoparticle showed a peak attributableto crystalline gold. From the shape of the peak, the size of the crystalwas found to be 2.6 nm. ICP analysis revealed that the content of goldwas 8.2 wt %. The p-ATP-coated gold nanoparticles were combined withelectrically conductive PANi as detailed in Example 1 except that thegold content based on PANi was 0.3 wt %. The electric conductivity wasmeasured as detailed in Example 1 and is shown in Table 2.

Example 7

A p-ATP-coated gold nanoparticle obtained as detailed in Example 6 wascombined with PANi during polymerization of the PANi as follows. 3.137 g(3.4×10⁻² mol) of aniline (obtained by distilling commercially availableaniline under reduced pressure) and 0.383 g of the p-ATP-coated goldnanoparticles were mixed. The mixture was added to 43 mL of 1 Mhydrochloric acid with 9.0 g of LiCl dissolved therein and mixed at −10°C. for 3 hours. Thereafter, 41 mL of an aqueous solution having 11.53 g(5.1×10⁻² mol) of ammonium persulfate dissolved therein was added dropwise to the solution under stirring at −10° C. over 30 minutes. Stirringwas continued at −10° C. for 24 hours, and the obtained precipitate wasrecovered. The precipitate was washed, rinsed with aqueous ammonia,washed again and then dried to obtain PANi at a yield of 95.5%. ICPanalysis revealed that the content of gold in the obtained PANi was 0.3wt %.

Next 250 mg of the p-ATP-coated gold nanoparticle-PANi mixture and 290mg of CSA were mixed in an agar mortar. 24.8 g of m-cresol was added andthe mixture was mixed thoroughly. This solution was coated on a glasssubstrate and dried to obtain a PANi film. The electric conductivity wasmeasured as detailed in Example 1 and is shown in Table 2.

TABLE 2 Comparative Example 6 Example 7 Example 1 Protective Agent:Gold20:1 20:1 — (Mole ratio) Gold content in PANi 0.3 0.3 0 (wt %) Electricconductivity 243 303 191 (S/cm)

Example 8

An aniline moiety-containing Polymer Protective Agent P(VP-ANi) havingthe structure given below was synthesized as follows.

30.4 g of N-vinylpyrrolidone (NVP, Nippon Shokubai Co., Ltd., Osaka,Japan) and 1.60 g ofN-phenyl-N′-(3-methacryloyloxy-2-hydroxypropyl)-p-phenylenediamine(NOCRAC G-1, Ouchi Shinko Chemical Industrial Co., Ltd., Tokyo, Japan)were charged into a 200 mL glass-made reaction vessel equipped with astirrer, a condenser and a nitrogen inlet tube. 48 g of 1,3-dioxolan(DOL, Osaka Organic Chemical Industry Ltd., Osaka City, Japan) was thenadded and dissolved. The atmosphere of the solution was purged withnitrogen and then the solution was heated, with stirring, to a solutiontemperature of 65° C. 0.32 g of dimethyl 2,2′-azobis(2-methylpropionate)(V-601) was then added as a polymerization initiator, and the reactionwas allowed to proceed for 20 hours. The reaction solution was thenadded drop wise into a large excess of acetone, and the precipitate wasrecovered. By ¹³C-NMR measurements, production of a copolymer wasconfirmed, and the copolymerization ratio of vinylpyrrolidone in thecopolymer was found to be 93.5 mol %. Other copolymers differing in thecopolymerization ratio were polymerized using the same method. Thecharge mass ratio and the solvent used in the polymerizations are shownin Table 3.

TABLE 3 Charge Mass Ratio NVP G-1 V-601 (NPV/G-1) (g) (g) (g) SolventUsed 95/5  30.4 1.6 0.32 DOL 90/10 28.8 3.2 0.32 DOL 75/25 24 8 0.32methanol 50/50 50 50 0.32 methanol

Example 9

A P(VP-ANi)-coated gold nanoparticle was synthesized as detailed inComparative Example 2 except that the P(VP-ANi) was synthesized with amass ratio of NPV/G-1 of 95/5 and the mole ratio of P(VP-ANi) to goldion (Au³⁺) in the solution before reduction of the gold ion was 0.1:1.X-ray diffraction measurements of the obtained P(VP-ANi)-coated goldnanoparticle showed a peak attributable to crystalline gold. From theshape of the peak, the size of the crystal was found to be 11.3 nm. ICPanalysis revealed that the content of gold was 98.7 wt %. ThisP(VP-ANi)-coated gold nanoparticle was combined with electricallyconductive PANi as detailed in Example 1 except that the gold contentbased on PANi was 1.1 wt %. The electric conductivity and Seebeckcoefficient were measured as detailed in Example 1, and the results areshown in Table 4.

Examples 10 to 13

A P(VP-ANi)-coated gold nanoparticle obtained as detailed in Example 9was combined with electrically conductive PANi as detailed in Example 1except that the gold content based on PANi was changed as shown in Table4. The electric conductivity and Seebeck coefficients were measured asdetailed in Example 1, and the results are shown in Table 4.

Example 14

A P(VP-ANi)-coated gold nanoparticle was synthesized as detailed inExample 9 except that the mole ratio of P(VP-ANi) to gold ion (Au³⁺) inthe solution before reduction of the gold ion was 1:1. X-ray diffractionmeasurements of the obtained P(VP-ANi)-coated gold nanoparticle showed apeak attributable to crystalline gold. From the shape of the peak, thesize of the crystal was found to be 6.9 nm. ICP analysis revealed thatthe content of gold was 76.0 wt %. This P(VP-ANi)-coated goldnanoparticle was combined with electrically conductive PANi as detailedin Example 1 except that the gold content based on PANi was 1.9 wt %.The electric conductivity and Seebeck coefficient were measured asdetailed in Example 1 and are shown in Table 4.

Example 15

A P(VP-ANi)-coated gold nanoparticle obtained as detailed in Example 14was combined with electrically conductive PANi as detailed in Example 1except that the gold content based on PANi was 5.6 wt %. The electricconductivity and Seebeck coefficient were measured as detailed inExample 1 and are shown in Table 4.

Example 16

A P(VP-ANi)-coated gold nanoparticle obtained as detailed in Example 14was combined by mixing the P(VP-ANi)-coated nanoparticle during thepolymerization of polyaniline as detailed in Example 7 except that thegold content based on PANi was 1.6 wt %. The electric conductivity andSeebeck coefficient were measured as detailed in Example 1, and theresults are shown in Table 4.

Comparative Example 3 Metal Nanoparticle-PANi Composite Using AnilineMoiety-Free Protective Agent

A PVP-coated gold nanoparticle synthesized as detailed in ComparativeExample 2 was combined with electrically conductive PANi as detailed inComparative Example 2 except that the gold content based on PANi was 9.9wt %. The electric conductivity and Seebeck coefficient were measured asdetailed in Example 1, and the results are shown in Table 4.

TABLE 4 Comparative Example Example 9 10 11 12 13 14 15 16 1 2 3Protective agent:gold 0.1:1 0.1:1 0.1:1 0.1:1 0.1:1 1:1 1:1 1:1 — 1:11:1 (Mole ratio) Gold content based 1.1 2.1 4.0 6.0 10.1 1.9 5.6 1.6 02.0 9.9 on wt of PANi (%) Electric conductivity 364 346 365 350 338 313285 241 191 219 230 (S/cm) Seebeck coefficient 13.0 13.7 13.6 13.6 13.313.5 12.1 12.7 13.4 11.8 11.9 (μV/K)

Example 17

A thermoelectric device was produced as follows by using CSA-doped PANias an electrically conductive polymer.

PANi was produced as detailed in Example 1. 0.25 g of PANi and 0.29 g ofCSA were mixed in an agate mortar, and 24.8 g of m-cresol was addedthereto and mixed thoroughly. This solution was coated on a substrate(having a release treatment), dried and separated from the substrate toproduce a PANi film having a thickness of 100 μm. The electricconductivity of the obtained PANi film was 191 S/cm, and the Seebeckcoefficient was 13.4 μV/K (both were measured as detailed in Example 1).

The PANi film was cut into a strip of 1 mm (width)×20 mm (length), andadhered at intervals of 2 mm on the self-adhesive surface of a polyimidetape having a self-adhesive layer. The oblateness of the cross sectionof the PANi film was 10 (=1 mm/100 μm). This PANi film was combined witha copper wire having a diameter of 0.1 mm and a length of 20 mm to forma unit thermocouple. The connection of the PANi film and the copperwire, was accomplished with an electrically conductive paste (XC-32,Fujikura Kasei Co., Ltd., Tokyo, Japan). Ten pairs of unit thermocoupleswere formed on the polyimide film and connected in series to fabricate athermoelectric device. The electric conductivity of copper is 6.0×10⁵S/cm, and the Seebeck coefficient is 1.8 μV/K.

A plurality of electrical connection portions arranged and aligned onone side of the thermoelectric device above were contacted as a hotjunction with a heater, and power generation was performed at roomtemperature. When the hot junction temperature was 179° C., thetemperature of another plurality of electrical connection portions, thatis, the cold junction temperature, was 38° C., which was a sufficientlylarge temperature difference between the two junctions. The outputvoltage at this time was 10.0 mV.

Example 18

A solution of PANi obtained as detailed in Example 17 was coated on apolyimide film by screen printing. Eight square PANi patterns of 30 mm(width)×30 mm (length) having a film thickness of 12 μm were formed atintervals of 10 mm. The electric conductivity of this PANi pattern was16.5 S/cm, and the Seebeck coefficient was 13.4 μV/K. The oblateness ofthe PANi pattern was 2,500 (=30 mm/12 μm). This PANi pattern wascombined with a copper wire having a diameter of 0.1 mm and a length of30 mm to form a unit thermocouple. The PANi pattern and copper wire wereelectrically connected using an electrically conductive paste, XC-32.Eight pairs of unit thermocouples were formed on the polyimide film. 64sheets of this film were further stacked, forming 512 pairs of unitthermocouples, which were connected in series to fabricate athermoelectric device. The electric conductivity of copper is 6.0×10⁵S/cm, and the Seebeck coefficient is 1.8 μV/K.

A plurality of electrical connection portions arranged on one side ofthe stacked thermoelectric device above were contacted as a hot junctionwith a heater, and power generation was performed at room temperature.When the hot junction temperature was 130° C., the temperature ofanother plurality of electrical connection portions, that is, the coldjunction temperature, was 70° C., which was a sufficiently largetemperature difference between the two junctions. The output voltage atthis time was 0.14 V, and the output current was 2.1 μA.

Example 19

Polyaniline (Ormecon NX-C002NB, Nissan Chemicals Industries, Ltd.,Tokyo, Japan) was coated on a polyimide film substrate and dried toobtain a 62 μm-thick polyaniline film. The electric conductivity of thispolyaniline film was 150 S/cm, and the Seebeck coefficient was 13.4μV/K. This film and the substrate were cut into a strip of 1 mm(width)×40 mm (length), and adhered at intervals of 2 mm on theself-adhesive surface of a polyimide tape having a self-adhesive layer.The thermal conductivity of the electrically conductive polyaniline hasbeen reported to be from 0.02 to 0.24 W/(m·K) (27° C.) (see, H. Yan, etal., J. Therm. Anal. Cal., 69, 881 (2002)).

A nickel foil (thickness: 20 μm) was cut into a strip of 1 mm (width)×40mm (length) and placed between polyaniline strips on the self-adhesivesurface of the polyimide tape. One end part of the polyaniline and oneend part of the nickel foil were electrically connected using anelectrically conductive paste (XC-32) to form a unit thermocouple. Tenpairs of unit thermocouples were provided on the polyimide film, andthese unit thermocouples were connected in series to fabricate athermoelectric device. The electric conductivity of nickel is 1.5×10⁵S/cm, the Seebeck coefficient is −23.2 μV/K (27° C.), and the thermalconductivity is 90.5 W/(m·K).

A plurality of electrical connection portions arranged on one side ofthe thermoelectric device above were contacted as a hot junction with aheater, and power generation was performed at room temperature. When thehot junction temperature was 105° C., the temperature of anotherplurality of electrical connection portions, that is, the cold junctiontemperature, was 25° C., which was nearly the same as room temperature,and was a sufficiently large temperature difference between the twojunctions. The output voltage at this time was 20 mV.

The temperature distribution on the thermoelectric device surface wasmeasured along the heat flow direction from the hot junction to the coldjunction. At distances of 0 cm, 1 cm, 2 cm, 3 cm and 4 cm from the hotjunction, the temperature on the thermoelectric device surface was 105°C., 48° C., 35° C., 29° C. and 25° C., respectively.

Example 20

A stacked thermoelectric device having the same structure as that inExample 18 having the p-ATP-coated metal nanoparticle-electricallyconductive PANi composite of Example 4 is theoretically examined.

From the experimental results of Example 18, the value of the deviceresistance can be calculated by dividing the output voltage by theoutput current to give a value of 66.7 kΩ (=0.14 V/2.1 μA). Theresistance of the unit thermocouple calculated based on the electricconductivity of PANi used is 25.9 kΩ in total, and therefore, thecontact resistance, between electrodes in the device can be estimated tobe 40.8 kΩ in total. The calculation formulas used for the estimationsare as follows.

Resistance  of  unit  thermocouple = resistance  of  PANi + resistance  of  copper  wire = (1/electric  conductivity  of  PANi  (S/cm)) ⋅ (length  (cm)/cross-sectional  area  (cm²)) + (1/electric  conductivity  of  copper  (S/cm)) ⋅ (length  (cm)/cross-sectional  area  (cm²)) = (1/16.5) × (3/3 × 12 × 10⁻⁴) + (1/5.99 × 10⁵) × (3/7.85 × 10⁻⁵) = 50.5  Ω + 0.0638  Ω = 50.6  ΩTotal  contact  resistance  in  device = total  resistance  of  device − total  resistance  of  unit  thermocouples = 66.7  k Ω − 512  (pairs) × 50.6  Ω = 66.7  k Ω − 25.9  k Ω = 40.8  k Ω

Using the results above, calculation when the material (PANi) used inExample 18 is replaced by the p-ATP-coated metal particle-PANi compositeof Example 4 is performed. The preconditions for the calculation are asfollows:

(i) the Seebeck coefficient does not change and in turn, the outputvoltage of the thermoelectric device does not change,

(ii) the contact resistance in the thermoelectric device does notchange, and

(iii) the value of 382 S/cm in Example 4 is used as the electricconductivity of the p-ATP-coated metal nanoparticle-PANi composite.

The calculation results are as indicated below.

Resistance  of  unit  thermocouple = resistance  of  composite + resistance  of  copper  wire = (1/electric  conductivity  of  composite  (S/cm)) ⋅ (length  (cm)/cross-sectional  area  (cm²)) + (1/electric  conductivity  of  copper  (S/cm)) ⋅ (length  (cm)/cross-sectional  area  (cm²)) = (1/382) × (3/3 × 12 × 10⁻⁴) + (1/5.99 × 10⁵) × (3/7.85 × 10⁻⁵) = 218  Ω + 0.0638  Ω = 2.24  ΩTotal  resistance  of  unit  thermocouples = 512  (pairs) × 2.24  Ω = 1.15  kΩDevice  resistance = total  resistance  of  unit  thermocouples + contact  resistance = 1.15  k Ω + 40.8  k Ω = about  42.0  k ΩOutput  current = 140  mV/42.0  k Ω = 3.3  µA

It is therefore predicted that when the metal nanoparticle-electricallyconductive composite material of Example 4 is used for the stackedthermoelectric device of Example 18, the output current becomes about1.6 times (3.3 μA/2.1 μA) larger.

We claim:
 1. A thermoelectric device comprising: (a) a heat resistantsubstrate; (b) a first thermoelectric material comprising anelectrically conductive polymer, wherein the first thermoelectricmaterial is disposed in a thin film on said substrate, (c) a secondthermoelectric material comprising an n-type semiconductor or a metal,wherein the second thermoelectric material is disposed in a thin film orwire shape on said substrate, wherein the second thermoelectric materialis adjacent to and spaced apart from said first thermoelectric materialand wherein said first and second thermoelectric materials togetherconstitute a unit thermocouple, and (d) an electrically conductivematerial that electrically connects an end part of said firstthermoelectric material and an end part of said second thermoelectricmaterial, thereby forming a circuit wherein said first thermoelectricmaterial and said second thermoelectric material are alternatelyelectrically connected in series and both ends of the circuit areopened.
 2. The thermoelectric device according to claim 1, wherein saidelectrically conductive polymer is polyaniline.
 3. The thermoelectricdevice according to claim 1, wherein said first thermoelectric materialfurther comprises a metal nanoparticle.
 4. The thermoelectric deviceaccording to claim 1, wherein said substrate is flexible.
 5. Thethermoelectric device according to claim 3, wherein said metalnanoparticles comprise gold, platinum, palladium, silver, rhodium,nickel, copper, tin, or an alloy thereof.
 6. The thermoelectric deviceaccording to claim 3, wherein said electrically conductive polymercomprises polyaniline, wherein said first thermoelectric materialfurther comprises a protective agent comprising 4-aminothiophenol,2-aminothiophenol, 3-aminothiophenol, 2-aminobenzenesulfonic acid,2-aminobenzoic acid, 3-aminobenzoic acid, 4-aminobenzoic acid,2-aminobenzonitrile, 3-aminobenzonitrile, 4-aminobenzonitrile,2-aminobenzyl cyanide, 3-aminobenzyl cyanide, 4-aminobenzyl cyanide,N-phenyl-1,2-phenylenediamine, N-phenyl-1,4-phenylenediamine, or acopolymer of N-vinylpyrrolidone, orN-phenyl-N′-(3-methacryloyloxy-2-hydroxypropyl)-p-phenylenediamine, andwherein said metal nanoparticles are coated with said protective agent.7. The thermoelectric device according to claim 3, wherein saidelectrically conductive polymer comprises polythiophene orpolythienylenevinylene, wherein said first thermoelectric materialfurther comprises a protective agent comprising3-(2-thienyl)-DL-alanine, 4-(2-thienyl)butyric acid,2-(2-thienyl)ethanol, 2-(3-thienyl)ethanol, 2-thiopheneacetic acid,3-thiopheneacetic acid, 2-thiopheneacetonitrile,2-thiophenecarbonitrile, 2-thiophenecarboxamide, 2-thiophenecarboxylicacid, 3-thiophenecarboxylic acid, 2-thiophenecarboxylic acid hydrazide,2,5-thiophenedicarboxylic acid, 2-thiopheneethylamine,2-thiopheneglyoxylic acid, 2-thiophenemalonic acid, 2-thiophenemethanol,or 3-thiophenemethanol, and wherein said metal nanoparticles are coatedwith said protective agent.
 8. The thermoelectric device according toclaim 3, wherein said electrically conductive polymer comprisespolypyrrole, wherein said first thermoelectric material furthercomprises a protective agent comprising pyrrole-2-carboxylic acid or1-(2-cyanoethyl)pyrrole, and wherein said metal nanoparticles are coatedwith said protective agent.
 9. The thermoelectric device according toclaim 1, wherein said n-type semiconductor comprises alloy-basedthermoelectric materials or oxide-based thermoelectric compounds. 10.The thermoelectric device according to claim 1, wherein said n-typesemiconductor comprises scutterdite compounds, silicide-based compounds,half-heusler metals, or boron compounds.
 11. The thermoelectric deviceaccording to claim 1, wherein said n-type semiconductor comprises zincoxide compounds, titanium oxide compounds, or nickel oxide compounds.12. The thermoelectric device according to claim 1, wherein said metalcomprises copper, nickel, or platinum.
 13. The thermoelectric deviceaccording to claim 1, wherein said second thermoelectric material thinfilm is formed by dispersing said n-type semiconductor or metal in aresin.
 14. The thermoelectric device according to claim 1, wherein saidsecond thermoelectric material thin film comprises a foil.
 15. Thethermoelectric device according to claim 1, wherein said secondthermoelectric material thin film comprises a thickness of about 1millimeter or less.
 16. The thermoelectric device according to claim 15,wherein said second thermoelectric material thin film comprises athickness of about 0.5 millimeters or less.
 17. The thermoelectricdevice according to claim 1, wherein the thermoelectric device is astacked thermoelectric device further comprising a plurality ofsubstrates, each substrate having disposed thereon at least one unitthermocouple.